Add link "get", "post", "put", "patch" and "delete" options

[reinink]

With the addition of the new as Inertia link option (#271), it has me rethinking the use of href for defining the URL for Inertia links. Previously this seemed fine, but now that Inertia links can be different element entirely, such as a div or a button, this no longer feels right.

Vue Router and React Router use the to attribute instead of href, which isn't bad:

<inertia-link to="/logout" method="post" as="button" type="button">Logout</inertia-link>

However, speaking with @nunomaduro, he had another interesting idea. What if instead of using the href or to, we instead had method specific attributes. For example:

<inertia-link get="/users">Users</inertia-link>
<inertia-link post="/logout">Logout</inertia-link>
<inertia-link delete="/users/1">Delete</inertia-link>
<inertia-link put="/users/1" :data="data">Update</inertia-link>
<inertia-link patch="/users/1" :data="data">Update</inertia-link>

I really like how this reads. Not only does it solve the href issue, it also allows you to define the method and URL using one attribute. 👌

And, of course, we would maintain support for the href and method attributes for backwards compatibility.